1. Field of the Invention
This invention is directed to methods for reducing aggregate and/or sediment formation in aqueous fixed copper based compositions containing Fe.sup.+3 and to compositions produced by these methods.
2. State of the Art
The use of copper based compositions for agricultural uses is well known in the art. Such compositions are employed as bactericidal and/or fungicidal compositions and all of these compositions rely upon the toxic action of the free Cu.sup.+2 ion (as opposed to chelated copper) which must penetrate into the microorganism in order to exert its toxic effect.
These copper based compositions are typically aqueous "fixed" copper based compositions because the copper compounds used in these compositions typically have a solubility of free Cu.sup.+2 from about 1 to 30 ppm in the aqueous solution with the remainder (and the vast majority) of the copper either being insoluble or in chelated form (i.e., "fixed"). The 1 to 30 ppm of Cu.sup.+2 in such aqueous compositions is typically referred to as "free copper" to distinguish it from either the chelated Cu.sup.+2 or the insoluble Cu.sup.+2 in these fixed copper compositions.
Because of their widespread use, some fungal and bacterial microorganisms have developed a dose dependent tolerance to aqueous fixed copper based fungicidal and/or bactericidal compositions. That is to say that such microorganisms are tolerant to fixed copper based fungicidal and/or bactericidal compositions at doses of free copper heretofore generally employed. At higher dosages, the increased amount of free copper in these compositions still exerts its toxic effect. However, the use of such higher dosages is not preferred for both economical and practical reasons.
As noted in allowed U.S. patent application Ser. No. 07/644,997 (U.S. Pat. No. 5,202,353), the use of up to about 300 ppm of Fe.sup.+3 in fixed copper based fungicidal and bactericidal compositions synergistically enhances the toxic activity of the free Cu.sup.+2 ions against fungi and bacteria. U.S. Patent application Ser. No. 07/644,997 is incorporated herein by reference in its entirety.
Notwithstanding the benefits of employing up to 300 ppm of Fe.sup.+3 with fixed copper based fungicidal and bactericidal compositions, it has now been found that upon addition of Fe.sup.+3 to fixed copper compositions, aggregates and/or sediment can form. Without being limited to any theory, it is believed that aggregation and sedimentation are related to the extent that formation of sufficiently large aggregates is a precursor of sediment formation and hence sediment formation is an extreme example of large aggregate formation.
In any event, aggregate and/or sediment formation is highly undesirable because they form larger particles whereas small particles are preferably delivered to the plant (the bacterial or fungal growth habitat) so as to obtain adequate coverage.
Accordingly, methods to inhibit formation of such aggregates and/or sediment and aqueous fixed copper based compositions containing Fe.sup.+3 wherein aggregate and/or sediment formation is reduced would be highly desirable.